Algal Biorefinery

Developments, Challenges and Opportunities

Ajay K. Dalai, Vaibhav V. Goud, Sonil Nanda, Venu Babu Borugadda, Ajay K. Dalai, Vaibhav V. Goud, Sonil Nanda, Venu Babu Borugadda

• Publisher: Routledge
• Year: 2021
• ISBN:
  9781000410839
• Edition: 1
• Topic: Business
• Subtopic: Industria energetica
• Index: Business

This book enables readers to understand the theoretical aspects, key steps and scientific techniques with a detailed mechanism to produce biofuels from algae.

Each chapter provides the latest developments and recent advancements starting from algal cultivation techniques to the production of value-added green fuels, chemicals and products with wide applications. The volume brings together a broad range of international and interdisciplinary experts, including chemical and biological engineers, biotechnologists, process engineers, environmentalists, pharmacists and nutritionists, to one platform to explore the beneficial aspects and challenges for an algal-based biorefinery. Chapters address cutting-edge issues surrounding algal cultivation, including genetic modification of algal strains, design and optimization of photobioreactors and open-pond systems, algal oil extraction techniques and algal-derived fuel products (biodiesel, bio-gasoline, jet fuels and bio-oil). Finally, the book considers the potential environmental impacts for establishing a sustainable algal biorefinery through lifecycle analysis, techno-economic assessment and supply chain management.

This book will be an important resource for students, academics and professionals interested in algal cultivation, biofuels and agricultural engineering, and renewable energy and sustainable development more broadly.

1 Algae as a bioresource for clean fuels, carbon fixation and wastewater reclamation

Kang Kang, Sadegh Papari, Hanieh Bamdad, Sonil Nanda, Ajay K. Dalai, and Franco Berruti

Introduction

Energy is necessary for the progression of human society. The high consumption of fossil energy sources, e.g., petroleum, coal and natural gas, has created serious issues regarding the future energy supply and environmental sustainability and safety. Although fossil energy is still the primary contributor to the global energy portfolio with nearly 80% of all energy sources, tremendous innovations achieved in alternative energy and increasingly serious environmental concerns have stimulated considerable interest in the exploration and exploitation of renewable energy sources (Zou et al., 2016). Biomass as an alternative energy source is playing a critical role in mitigating global warming (Jin et al., 2019). Due to its abundance and carbon neutrality, biomass shows great potential as an energy resource in social, economic and environmental terms.

After years of development, the first generation of biofuels produced using edible feedstocks, such as grains, seeds, plant oils, sugar and starch, had been demonstrated to have limitations in sustainability and efficiency (Mohr and Raman, 2013). The second-generation biofuels are based on more efficient renewable feedstocks, such as inedible lignocellulosic biomass, including agroforestry residues, sawdust and municipal solid wastes, which overcomes the drawbacks of the first generation (Nanda and Berruti, 2021a, 2021b; Okolie et al., 2021). However, more research efforts are required to achieve a competitive cost (Alalwan et al., 2019). Land-intensive bioenergy is limited by the constraint of land area and often leads to high carbon emissions due to land-use change, biomass production, harvesting and transportation (Reid et al., 2020). Therefore, land-intensive bioenergy functions reasonably well as a transitional element of the global energy matrix, playing an important role over the next few decades, and then might fade in the long run. While optimizing feedstock cultivation, conversion technology and utilization options of the second-generation biofuels, research interests in third-generation biofuels are now booming (Figure 1.1).

Figure 1.1 Feedstock for different generations of biofuels.

There are several benefits of considering algae as the better biomass feedstock. Firstly, algae are fast-growing organisms that can transform one-tenth of the solar energy into biomass, and the theoretical yield can reach approximately 77 g of biomass/m²/day under the conditions of average sunlight irradiance (Khan et al., 2018). It was reported that nearly 13 kg dry weight/m2 of brown algae could be produced within 7 months under the planting conditions that could produce sugarcane at the rate of 6.1–9.5 kg fresh weight m²/year (Kraan, 2013). Secondly, as photosynthetic organisms, algae accumulate energy via the photosynthesis process, so the utilization of this energy under ideal conditions is not expected to increase the gross level of CO₂ in the atmosphere. In addition, compared to lignocellulosic biomass, algae could be cultivated within freshwater or saltwater bodies and can grow on infertile or marginal lands. Therefore, they are significantly less land-intensive. Since approximately 71% of the earth’s surface is water-covered, algae win a tremendous edge in terms of location for cultivation. Moreover, the production of algae does not compete with land for cultivating food crops, and algae could efficiently utilize the water and fertilizers and are capable of producing high oil and biomass yields (Jones and Mayfield, 2012).

Algal biomass is a highly versatile feedstock and can be converted into various types of biofuels, such as bioethanol, biodiesel, bio-oil, biogas and biochar, via a range of biological and thermochemical conversion techniques (Rastogi et al., 2018). Other strategies, e.g., catalytic treatments, are also being investigated to convert algal biomass. To produce the algal biomass, both commercial and research activities are globally booming toward commodity algal-based products. Algae have attracted significant interest recently for their potential commercial utilization in the production of biofuels and nutritional supplements (Chang et al., 2011).

Currently, the most feasible way of the utilization of algal biomass is the conversion into liquid fuels with comparable fuel quality to conventional diesel. In combination with innovative techniques of using different types of solid wastes as fertilizers, the productivity and cost-effectiveness of algal-based liquid fuels will continue to improve (Campbell, 2008). Currently, the advantages of algal-based fuels have not been fully proven to justify large-scale algal cultivations, since the production costs are still high (Vassilev and Vassileva, 2016). Besides, the high water content causes low energy density of the un-processed algal biomass and increases the capital and operating costs for dewatering and transportation of the raw algae. In light of this, metabolic engineering might likely become a key solution in strain development to optimize the solar conversion efficiency of algae and form the basis for a fourth-generation biofuel production (Lü et al., 2011).

To comprehensively discuss the utilization of algae as a renewable energy and materials source, this chapter introduces the metabolism and physicochemical characteristics of algae. Furthermore, the progress made in converting algae into clean fuels using physicochemical, thermochemical and biological technologies is discussed. Finally, the advancements of using algae in environmental applications, such as biological carbon fixation and wastewater treatment, are reviewed.

Algal metabolism and high-lipid-containing algal strains

Algal metabolism

Algae are eukaryotic organisms, which belong to the Protista kingdom. Their cells consist of a nucleus and other organelles encapsulated in membranes. Algae can be categorized as macroalgae and microalgae. Macroalgae are multicellular and relatively larger in size compared to the unicellular microscopic microalgae. Based on their pigmentation, macroalgae could be classified into three broad groups, including red seaweed (Rhodophyceae), brown seaweed (Phaeophyceae) and green seaweed (Chlorophyceae) (Demirbas, 2010). Microalgae are a diverse group of aquatic organisms that include more than 50,000 photosynthetic types of microorganisms that can perform photosynthesis, reproduce quickly and survive in difficult growing environments (Adenle et al., 2013). The unicellular green algae Chlamydomonas have a simple lifecycle and provide easy isolation of mutants and a growing array of technologies for molecular genetic research (Harris, 2001).

During the growth phase, algae can adapt in both freshwater and saltwater. In addition, excellent flexibility allows them to live under different cultivation conditions. Microalgae cultivation with sunlight as an energy source can be carried out in ponds or photobioreactors (PBRs) designed according to tubular, flat plate or other configurations (Demirbas, 2010). Nutrient supply can also be achieved through the circulation of water from neighboring lands or by feeding the water from local wastewater treatment plants. This enables certain types of algae to be cultivated in contaminated water followed by their use as a feedstock for lipid extraction or conversion to biofuels. As proposed by De Bhowmick et al. (2019), a ‘zero waste discharge’ can be achieved with the simultaneous production of biofuel, biochar and other high-value products while keeping the greenhouse gases’ impacts at very low levels.

Algae produce their nourishment via the photosynthesis process, during which the solar energy and atmospheric CO₂ are transformed into carbohydrates and oxygen. For their cultivation, CO₂ sources could be effluent from power plants or chemicals in different forms, e.g., soluble carbonates, including Na₂CO₃ and NaHCO₃ (Brennan and Owende, 2010). A deeper understanding of the light-absorbing mechanism and its effect on cellular systems facilitates the basic scientific research and commercialization of the photosynthetic organisms.

High-lipid-containing algal strains

The suitability of algae as fuel precursors is determined by many critical factors. The evaluation can be performed using parameters including growth rate, photosynthetic yield, biomass productivity and carbohydrate content (Sirajunnisa and Surendhiran, 2016). Due to the huge diversity, the screening of algae is one of the most important tasks to assess potential fuel production. Some of the processes used for lipid extraction from algae include mechanical methods, ultrasound, microwave, pulsed-electric field, surfactants, organic solvents, supercritical fluids (SCF), ionic liquids and deep eutectic solvents. The recovery and purification of lipids from algal cells via a few promising technologies could be a barrier due to substantial cost and energy requirement.

Lipid extraction from wet algae involves the disruption of the algal cell walls in the cultivation solution, and such process can be grouped into organic solvent-based and solvent-free approaches (Naghdi et al., 2016). During the solvent-based lipid extraction procedure, water acts as a barrier between the intracellular lipids and nonpolar organic solvents; therefore, the efficiency could be enhanced by increasing the polarity of the solvent. To deal with potential safety and environmental concerns, organic solvent-free methods have been developed and those that can be used for various algal strains with reasonable energy consumption and infrastructure are highly desirable. Some of the recently published results are given in Table 1.1.

Table 1.1 Summary of...